A glass chopped strand mat is conventionally used as a reinforcement member of a glass fiber reinforced plastic (GFRP) molded product, such as a bathtub or a septic tank. The glass chopped strand mat has in recent years been employed as a reinforcement base of an automotive molded ceiling material. The automotive molded ceiling material in which the glass chopped strand mat is attached to both sides of a foamed polyurethane sheet has been developed.
The glass chopped strand mat is produced as follows. Initially, a glass fiber is cut into pieces having a predetermined length to obtain glass chopped strands. Next, the glass chopped strands are distributed and deposited on a conveying means such as a conveyor to be formed into the shape of a sheet. The glass chopped strands are subjected to a plurality of steps while being conveyed by the conveyor. For example, the steps include spraying a binder to the glass chopped strands, heating the glass chopped strands with the adhering binder, and cooling and pressing the glass chopped strands after the heating, and the like. The glass chopped strand mat produced by these steps is wound around a core into a roll by a winding machine or the like before shipment.
The glass chopped strand mat which has been wound into a roll is processed into an automotive molded ceiling material as follows. The glass chopped strand mat is temporarily unwound. An adhesive is applied to the glass chopped strand mat. The glass chopped strand mat is wound again. Thereafter, the glass chopped strand mat with the adhesive, a foamed urethane sheet as a base member, and the like are attached together and molded into an automotive molded ceiling material having a desired shape.
In recent years, as the diversity of automotive design has increased, there has been a demand for a ceiling surface having a more complicated shape in order to further improve the design. To meet such a demand, the glass chopped strand mat used for a ceiling surface is required to have a high level of flexibility. The flexibility of the glass chopped strand mat is preferably increased by distributing glass chopped strands in the glass chopped strand mat as uniformly in all directions as possible. The flexibility may also be increased by reducing the amount of the binder added to the grass chopped strands. In these techniques, however, a sufficient tensile strength may not be imparted to the glass chopped strand mat, and in particular, when the glass chopped strand mat with the applied adhesive is temporarily unwound in the above-described process of producing the automotive molded ceiling material, the glass chopped strand mat may not withstand the tensile force and may be broken along the width direction.
Advances in automotive weight reduction have led to a demand for a reduction in the weight of the automotive molded ceiling material. This demand may be satisfied by reducing the weight of the glass chopped strand mat itself by reducing the amount of glass chopped strands which are used as a material for the glass chopped strand mat. However, when the weight of the glass chopped strand mat is reduced by reducing the amount of glass chopped strands, the tensile strength of the glass chopped strand mat obtained decreases, and therefore, the glass chopped strand mat is more likely to be broken in any process. The break of the glass chopped strand mat directly leads to a molding defect, an interruption of the producing process, or the like.
On the other hand, when the tensile strength of the glass chopped strand mat becomes excessive, the flexibility decreases, and therefore, when the automotive molded ceiling material is molded, a molding defect, such as a depression or a dimple, which is called a “sink mark,” is likely to occur in the surface of the automotive molded ceiling material. As a result, the yield of the automotive molded ceiling material deteriorates, leading to a decrease in production efficiency.
Therefore, it is necessary for the glass chopped strand mat used in the automotive molded ceiling material to have both a good flexibility and a good tensile strength.
Heretofore, a known glass chopped strand mat has a difference in tensile strength between the mat width direction and the mat longitudinal direction (see Patent Document 1). Patent Document 1 describes a method for producing a glass chopped strand mat which is formed of glass chopped strands having an average strand mass density of 10 to 20 tex, has a weight of 50 to 150 g/m2, an average tensile strength in the mat width direction of not more than 150 N which is measured in a tensile rupture test conducted under the Japanese Industrial Standards (Annex 13 of JIS R3420 (1999)), the standard deviation of the tensile strength being not more than 50 N, and an average tensile strength in the mat longitudinal direction of not less than 100 N. It is considered that this glass chopped strand mat has such good quality that it has a sufficient strength, and there is only a small risk of a problem with appearance, such as a pattern which stands out from the surface of a molded product in the shape of the glass chopped strand after the glass chopped strand mat is molded into an automotive molded ceiling material.
Note that Annex 13 of JIS R3420 (1999), which describes a “method for determining the tensile breaking force for textile glass mats,” is a translation of ISO 3342, “Textile glass—Mats—Determination of tensile breaking force,” Third Edition, 1995, where no subject matter is changed.